A group of Russian private military contractors have been killed in recent attacks by US warplanes in eastern Syria.

Russian media reports said Tuesday that the several Russians were helping the Syrian and Russian military in the drive against militants in the province of Dayr al-Zawr when they came under attack by the US forces last week.

Russia’s Defense Ministry said its troops were not involved in the incident while Kremlin spokesman Dmitry Peskov would not comment on the issue and said the report needed to be verified.

The reports said the military contractors were part of a Syria government offensive to take back control of oil fields in Dayr al-Zawr from militants.

The US military has confirmed that it has attacked pro-government forces in eastern Syria. It said in a statement last week that the operation came after some 500 pro-government forces attacked a group of US-backed opposition forces in the region. It said US advisors had a presence among the opposition group.

Russia has repeatedly accused the United States of trying to hamper a Syrian full victory against Daesh, a Takfiri terrorist group that is on its last legs in eastern Syria and in the neighboring Iraq. Moscow has released evidences showing that US forces stationed in Dayr al-Zawr’s border regions and in Jordan have been collaborating with Daesh and other militants through providing intelligence about Syrian and Russian forces.